The invention relates generally to internal combustion piston engines, fluid pumps and similar machines and, more particularly to an X-Engine configuration.
The objective of an engine designer is to provide the best function with regards to performance and efficiency, while also minimizing the amount of noise and vibration that emanate from the engine. It is also desirable to provide an engine that is the smallest, lightest-weight while having a design which can be economically manufactured and serviced.
The most widely used engine configurations in use and today are in-line, “V” and horizontally-opposed or ‘flat’. Almost all of these engines use conventional connecting rods (“con rods”) in the power conversion system. Con rods, due to the complex nature of their motion, produce multiple orders of vibration such that there is no practical way to cancel out all of the resultant vibration in an engine that has con rods. Some conventional engine configurations which use con rods, such as the 90° V-8 and the in-line-four cylinder with dual 2nd-order balancers, have balance for 1st-order and 2nd-order vibrations, but practically all engines with conventional con rods are never balanced for 3rd-order vibrations and above. Furthermore, as the engine runs con rods induce torsional loads on the crankshaft that typically are not fully resolved as a result of the engines' configuration or from the use of extra balancing mechanisms.
The Scotch yoke is a mechanism for converting the linear motion of a slider into rotational motion of a shaft or vice-versa, and has been demonstrated to be suitable for use in internal combustion piston engines. The piston or other reciprocating part is directly coupled to a sliding yoke with a slot that engages a pin on the rotating crankshaft, with a bearing block is fitted in between the crankshaft and the yoke to provide a cylindrical-cylindrical interface at the crankpin and flat-on-flat interface with the yoke so that the contact pressures at both interfaces are at acceptable levels. The shape of the motion of the piston is a pure sine wave over time given a constant rotational speed of the crankshaft.
So, unlike conventional engine configurations in use today, the scotch yoke mechanism is a mechanism that couples the reciprocating pistons to the rotating crankshaft with true harmonic motion for the reciprocating mass, assuming a constant rotational speed of the crankshaft, such that an engine that uses scotch yokes can be said to be “100% balanced for all orders” or “perfectly balanced” if it is balanced for 1st-order forces and moments.
With regards to reducing friction in an engine, the scotch yoke mechanism can be used in a double-ended or “double-acting” fashion such that each reciprocating assembly has a piston at either end, hence a benefit of the double-acting scotch yoke is that the fluid motion inside the crankcase is reduced because opposite pistons simply push air in between them, whereas in “V”-type engines and in-line engines there is a larger mass of fluid in motion inside the crankcase which is pushed out of the cylinders and around the engine's bulkheads in a way that causes larger amounts of fluid friction and necessitates having an empty volume in the engine crankcase to allow this fluid motion to occur. So, it can be seen that the Double-Acting Scotch Yoke system can provide an engine with reduced friction which translates to better fuel efficiency and better performance.
Another capability of the Double-Acting Scotch Yoke is that it can be used in an X-engine configuration having two reciprocating assemblies for a total of four pistons coupled to each crankpin bearing on the crankshaft in a similar way to the conventional connecting rod as it is used in V-configuration engines which have two con rod and piston assemblies coupled to each crankpin bearing on the crankshaft. By doubling the number of cylinders coupled to each crankpin bearing, and having no requirement to allow large amounts of fluid motion to pass across the main bearing support structure as the engine runs, the Double-Acting Scotch Yoke used in X-configuration can result in a significantly smaller and lower mass engine for a given bore & stroke and number of cylinders when compared with in-line, “V” and flat engine configurations.
It should also be noted that a radial engine that employs a master con rod with secondary con rods attached to it is an arrangement which allows multiple cylinders of an engine to be attached to a single crankpin bearing, but the compromise here is that there are at least two different piston motions (piston displacement versus crankshaft angle) occurring in this type of engine, which greatly complicates any efforts to achieve balance of even the 1st-order of vibration. Hence, there is no practical method to have 1st and 2nd order balance for a group of cylinders connected in this way. Furthermore, with the modern fuel injection systems used in engines now, having different piston motions would greatly complicate the calibration and emission-ability of such an engine.
Hence, the X-engine configuration using the double-acting scotch yoke—a mechanism that provides true ‘harmonic motion’—has the potential to provide a superior result for many piston engine applications, which today are mostly “V”, in-line, and flat engines that employ con rods.